We note that in our model, the CO released in the KB would be coming from pure CO ices and not CO trapped in water, CO\(_2\) , or other less volatile ices [1]}, which sublimation temperatures are too high to become gas at KB distances. Therefore, we only expect the most volatile species to be able to be released as gas in the KB. The volatiles with sublimation temperatures lower than 40 K are N\(_2\)  (22 K), O\(_2\)  (24 K), CO (25 K), and CH\(_4\)  (31 K) with the sublimation temperature given in parenthesis [2]}. The photodissociation timescales can also affect the observability of these species. At the KB, we find photodissociation timescales of 25-62 yr for N\(_2\) , 8-13 yr for O\(_2\) , 34-86 yr for CO and 3-8 yr for CH\(_4\)  [3]}. Now, we use the cometary abundances of volatiles as a proxy for the abundance of planetesimals in the KB. N\(_2\)  has been observed in a few comets from the ground [4]} and in-situ in 67 P [5]}. At most the N\(_2\) -to-CO ratio could be 0.06 [4]} in comets formed at large distances. N\(_2\)  would thus be even more difficult than CO to observe even though they have similar photodissociation timescales. O\(_2\)  has also been observed in the coma of 67 P showing that it may be as abundant as CO on the comet [7]}. O\(_2\)  photodissociates roughly 4 times as fast as CO at the KB and the daughter neutral oxygen species would accumulate to that created from CO if planetesimals in the KB routinely include O\(_2\)  ices. As for methane, the CH\(_4\) -to-CO ratio is roughly 0.1 [8]} and its photodissociation timescale at the KB is roughly 11 times smaller than for CO. Therefore, the released CH\(_4\)  would also be more difficult to observe than CO.
